Rubidium --82, a positron emitter with a half-life of 75-sec is readily obtainable from the parent Sr-82 (T.sub.1/2= 25 days). Rubidium can be used as a diffusible flow tracer for the myocardium and kidney, and as a nondiffusible tracer for brain blood flow. Serial injections of Rb-82 can be administered every 5 to 10 minutes by eluting (milking) Rb-82 from its 25-day Sr-82 parent. The advantages of Rb-82 are low radiation dose, ability to provide for repeated examinations every 5 minutes without constraints from body background, and a convenient and economical supply of a short-half-life positron emitter. (Yano et al, The Journal of Nuclear Medicine 20:961-966, 1979.)
Significant quantities of .sup.82 Sr are available for clinical investigation. The short-lived daughter, 75-second .sup.82 Rb, is of value in biomedicine for circulation and perfusion studies as well as for myocardial imaging as mentioned in U.S. Pat. No. 3,953,567.
Grant et al disclose partial resolution of inconsistencies in the medical literature regarding the performance characteristics of .sup.82 Sr/.sup.82 Rb radionuclide generators as discussed at page 1250 of Grant el al, The Journal of Nuclear Medicine, Vol. 19, Number 11; pages 1250-1254, 1978.
Yano et al, Journal of Nuclear Medicine, 18:46-50, 1977 disclose that two different ion-exchange resins loaded with spallation-produced .sup.82 Sr indicated that the Bio-Rex 70 Saline system was superior to the Chelex-100 NH.sub.4 Cl--NH.sub.4 OH system for the separation of .sup.82 Rb. Not only was the observed separation factor higher with Bio-Rex 70 resin, but a 2% saline solutin was also observed to be a better eluent for intravenous infusion than the 0.1 M NH.sub.4 OH--NH.sub.4 Cl buffer.
Yano et al in the International Journal of Applied Radiation & Isotopes, Vol. 30, pages 382-385, 1979, disclose breakthrough data for .sup.85 Sr batch studies with Al.sub.2 O.sub.3 adsorber using 2% NaCl, pH 8-9 eluent; Bio-Rex 70 adsorber using 2% NaCl, pH 8-9 eluent; and Chelex 100 adsorber using 0.1 M (NH.sub.4 Cl+NH.sub.4 OH), pH 9 eluent. Yano et al cite previous work with Bio-Rex 70, a weakly acidic cation resin and Chelex 100, a chelating ion exchange resin, which indicated that a good separation of .sup.82 Rb from .sup.82 Sr could be obrained; however, the former ion exchange resin exhibits an increase in .sup.82 Sr breakthrough after a moderate number of elutions with 2% NaCl at pH 7-8, while the latter resin requires an NH.sub.4 OH+NH.sub.4 Cl buffer at pH 9.0 as the eluent solution which is not desirable for intravenous infusion.
Rubidium and potassium are chemically related elements and are in the alkali-metals group of the periodic table. The biological behavior of Rb and K is very similar, both being taken up by muscle. Furthermore the myocardial uptake of Rb after intravenous infusion is related to the rate of blood flow through the myocardium. .sup.84 Rb, a positron-emitting isotope, has been used with coincidence gamma-ray counters to determine coronary blood flow in man. However, because of its relatively long half-life of 33 days and its high cost, .sup.84 Rb presents disadvantages for coronary blood-flow studies. .sup.82 Rb has physical characteristics that are suitable for visualizing deep-lying organs. It has a half-life of 75 sec and decays 96% of the time by positron emission with a maximum energy of 3.15 Mev. The positron is accompanied by a 0.77-Mev gamma ray (9.0% abundant) to the ground state of .sup.82 Kr. Its very short half-life offers low radiation exposure and the possibility of quick repeat studies. Because it is a positron emitter, the positron scintillatin camera, with its high sensitivity and excellent image-forming characteristics for deep-lying organs can be used; see Yano et al, Journal of Nuclear Medicine, volume 9, Number 7 pages 412-415; 1968.
.sup.82 Rb is produced continuously by decay of the parent isotope, .sup.82 Sr which decays with a half-life of 25 days. By use of a chromatographic column, .sup.82 Rb can be milked from the parent isotope every 5-10 , minutes.